A simple solution if you don't have flip-up lens caps, or have built in elastic bands!
Very useful on your scopes for airsoft, milsim/ woodsball paintball, or real steel guns.
Eliminates the need to take the time to remove individual caps and store them, but rather both as a unit, or to let them hang on the rail mounts for ease of access.

Step 1: The Materials

-Your lens caps (obviously)
-your optic
-some nylon elastic cord or paracord if you can't find the former!
-hobby knife or exacto knife
-soldering iron
-lighter

Step 2: Make Holes

Mark and cut out the holes, or if you so choose, you could melt them out with le soldering iron!
Then,measure out your elastic to about a half inch shorter than your optic on both sides (to create a loop) and thread your elastic through.

Step 3: Tie It Off

Tie off the standing ends inside one of the caps, or, if there isn't enough clearance inside then on the outside inbetween the two caps.
Make sure to use a strong knot! i used a fishermans knot, which is basically two linking overhand knots that tighten when pulled apart. This knot can also be used to vary tightness, VERY useful if you use paracord and not elastic cord
Then, use your lighter and melt the knots slightly to lock them in place.